In the continuing search for new compounds that can break drug resistance in bacterial infections of humans and other mammalian species, certain anti-bacterial peptides and glycopeptides isolated from insects have been noted as promising candidates for drug development [D. Hultmark, Trends Genet., 9:178–183 (1993); J. P. Gillespie et al, Annu. Rev. Entomol., 42:611–643 (1997)]. See, also, International Patent Application No. WO94/05787, published Mar. 17, 1999; French patent No. 2733237, granted Oct. 25, 1996; International Patent Application No. WO99/05270, published Feb. 4, 1999; International Patent Application No. WO97/30082, published Aug. 21, 1997; French patent No. 2695392 granted Mar. 11, 1994 and French patent No. 2732345, granted Oct. 4, 1996.
While many anti-bacterial peptides from other origins kill bacteria by disrupting the cell membrane or cell wall, some of the insect-derived anti-bacterial peptides have an unusual mode of action, i.e., they bind to a currently unknown, stereospecific target molecule [P. Bulet et al, Eur. J. Biochem., 238:64–69 (1996)]. Two such peptides are drosocin, a 19 amino acid residue peptide from species of Drosophila [P. Bulet et al, J. Biol. Chem., 268(20):14893–14897 (1993)] and pyrrhocoricin, a 20 amino acid residue peptide from species of Pyrrhocoris [S. Cociancich et al, Biochem, J., 300:567–575 (1994)]. Drosocin and pyrrhocoricin are glycopeptides characterized by the presence of a disaccharide in the mid-chain position. The presence of the sugar increases the in vitro anti-bacterial activity of drosocin, but decreases the activity of pyrrhocoricin [P. Bulet et al, 1996, cited above; R. Hoffmann et al, Biochim. et Biophys. Acta, 1426:459–467 (1999)].
Drosocin is moderately active against Gram-positive bacteria. When the native glycosylated drosocin is injected into mice, the glycopeptide shows no anti-bacterial activity, probably due to the peptide's rapid decomposition in mammalian sera [Hoffmann et al, 1999, cited above]. While drosocin needs 12–24 hours to kill bacteria in vitro, it is completely degraded in diluted human and mouse serum within a four-hour period. Both aminopeptidase and carboxypeptidase cleavage pathways (decomposition at both ends) can be observed.
Native pyrrhocoricin is also a glycosylated peptide. Pyrrhocoricin is more active against Gram-negative bacteria than drosocin, but the peptide is almost completely inactive against Gram-positive strains. Native pyrrhocoricin appears to be more resistant to mouse serum degradation than drosocin, but decomposes quickly in some batches of human serum.
Metabolites from serum stability assays of drososin and pyrrhocoricin were identified, and the metabolites, lacking as few as five amino terminal or two carboxy terminal amino acids are inactive [Bulet et al, 1996 and Hoffmann et al, 1999, both cited above). This is further supported by a recent model of the bioactive secondary structure of drosocin, which identifies two reverse turns, one at each terminal region, as binding sites to the target molecule [A. M. McManus et al, Biochem., 38(2):705714 (1999)]. The situation is further complicated by the fact that the degradation speed and pathway of a given peptide in diluted mouse sera are somewhat different from those observed in diluted human sera. Even different batches of human sera degrade the peptides at different rates and may yield different metabolites in vitro. The peptide's stability is markedly increased in insect hemolymph where the peptides manifest their biological functions [Hoffmann et al, 1999, cited above].
There exists a need in the art for novel anti-bacterial and anti-fungal compounds, novel anti-bacterial and anti-fungal pharmaceutical compositions and methods of use thereof, and novel compounds which can be employed in drug screening analyses to detect new pharmaceutical antibiotics.